Strapped-Down Attitude System SIAS-2


The SIAS-2 was initially developed for measuring yaw, pitch and roll of an airborne infrared scanner system mounted in a small aircraft. Due to its small physical size, low weight and reliable performance, the system is now available commercially for use in any aircraft or towed 'bird'.


gyroscopes and accelerometers

Inertial system consists of three Fizoptika fiber optic gyroscopes and three Analog Devices Inc. ADXL-series accelerometers. A GPS receiver for XYZ coordinates and time code is also integrated into the system.

Various sensor signals pass through a precision ADC and then to a digital signal processor. Data are transferred using Ethernet interface (TCP/IP).

Proprietary algorithms process the GPS and inertial data, yielding a high quality attitude solution automatically. For a whole flight, accuracy of yaw is about 2°, and for pitch and roll it is better then 1'. Sensitivity of the system is 1°. Moreover, we get smoothed geographic position, without discontinuities of standard GPS solution.

Angle of pitch
Fig. 2. Angle of pitch (green) and its high frequency component (red)

Figure 2 shows that the SIAS system detects even small vibrations of less then 3' at 16,5 Hz. Platform is the STOL airplane Cessna-172D.

Quality of correction of infrared image is illustrated with figure 3:

before correction after correction

Angles of yaw, pitch and roll
Angles of yaw (red), pitch (green) and roll (blue), Aircraft: Cessna-172D